1. Field of the Invention
The present invention relates to a method of manufacturing the SnZnNiCu solder powder having excellent joint reliability and the SnZnNiCu solder powder.
2. Description of Related Art
Conventionally, Sn—Pb alloy has been used as solder alloy. In recent years, however, due to concern about human health and the environment, Pb-free solder alloy containing no Pb has been developed. As the Pb-free solder alloy, for example, Sn—Ag solder alloy, Sn—Ag—Cu solder alloy and the like have been proposed. However, since these solder alloys have high melting point, heating temperature needs to be high during soldering and, in some cases, exceeds an allowable range of heat resistance of electronic parts. In addition, since Ag3Sn phase in solder grows large, strength of solder itself deteriorates.
On the other hand, Sn—Zn solder alloy has a potential means to solve the above problem, since Zn has the function of lowering a melting point and can lower heating temperature during soldering. For example, in each patent literature as below, various Sn—Zn solder alloys have been proposed.
Japanese Unexamined Patent Publication No. H8-243782 discloses Sn—Zn solder alloy containing 3 to 12% by weight of Zn and, as additional component, not more than 3% by weight of at least one selected from the group of Sb, In, Au, Ag and Cu. This solder alloy is considered to improve wettability during soldering by containing the above additional component.
Japanese Unexamined Patent Publication No. H9-94687 discloses Sn—Zn solder alloy containing 7 to 10% by weight of Zn, 0.1 to 3.5% by weight of Ag and/or 0.1 to 3% by weight of Cu. Japanese Unexamined Patent Publication No. H9-94688 discloses Sn—Zn solder alloy containing 7 to 10% by weight of Zn, 0.01 to 1% by weight of Ni, and 0.1 to 3.5% by weight of Ag and/or 0.1 to 3% by weight of Cu. These solder alloys are considered to improve tensile strength by containing the above additional component.
Japanese Unexamined Patent Publication No. H9-155587 discloses Sn—Zn solder alloy containing 7 to 9% by weight of Zn and 0.1 to 0.5% by weight of Cu. This solder alloy is considered to improve mechanical strength by containing the above additional component.
Japanese Unexamined Patent Publication No. 2000-15478 discloses Sn—Zn solder alloy containing not more than 0.5% by weight of an additional component such as Cu, Al and Ni. This solder alloy is considered to inhibit change in mechanical characteristics by containing the above additional component.
Japanese Unexamined Patent Publication No. 2001-259885 discloses Sn—Zn solder alloy containing 92 to 96% by weight of Sn, 1 to 5% by weight of Zn, 1 to 3% by weight of Cu and 0.5 to 2% by weight of Sb. This solder alloy is considered to achieve high joint strength.
By the way, soldering on Cu base material with the use of Sn—Zn solder alloy usually causes the problem that a thick fragile layer of Cu—Zn intermetallic compound is formed in the vicinity of the interface between the Cu base material and the solder alloy. Moreover, in soldering on Cu base material with the use of solder alloy which has Cu and the like added to improve mechanical strength and wettability as mentioned in each of the above patent literatures, addition of Cu to the solder alloy has made the intermetallic compound layer in the vicinity of the interface thicker. When such a Cu—Zn intermetallic compound layer is formed, joint strength between Cu base material and solder alloy and joint reliability deteriorate. The intermetallic compound layer further grows over time even after soldering, and along with the growth, joint reliability between Cu base material and solder alloy further deteriorates.